linux-kernel - Re: RFC: Petition Intel/AMD to add POPF

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Date:   Thu, 18 Aug 2016 19:49:10 +0200
From:   Denys Vlasenko <dvlasenk@...hat.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Andy Lutomirski <luto@...capital.net>,
        Sara Sharon <sara.sharon@...el.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Christian König <christian.koenig@....com>,
        Vinod Koul <vinod.koul@...el.com>,
        Alex Deucher <alexander.deucher@....com>,
        Johannes Berg <johannes.berg@...el.com>,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
        Andy Lutomirski <luto@...nel.org>,
        the arch/x86 maintainers <x86@...nel.org>,
        Ingo Molnar <mingo@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Adrian Hunter <adrian.hunter@...el.com>
Subject: Re: RFC: Petition Intel/AMD to add POPF_IF insn



On 08/18/2016 07:47 PM, Denys Vlasenko wrote:
> On 08/18/2016 07:24 PM, Linus Torvalds wrote:
>> That said, your numbers really aren't very convincing. If popf really
>> is just 10 cycles on modern Intel hardware, it's already fast enough
>> that I really don't think it matters.
>
> It's 20 cycles. I was wrong in my email, I forgot that the insn count
> also counts "push %ebx" insns.
>
> Since I already made a mistake, let me double-check.
>
> 200 million iterations of this loop execute under 17 seconds:
>
>   400100:    b8 00 c2 eb 0b           mov    $0xbebc200,%eax # 1000*1000*1000

Grr. It's 200*1000*1000, not one billion. Sorry.